A gas turbine has excellent features such as its compactness, high efficiency, low frictions due to no reciprocating portion, and durability to high temperatures due to no sliding portion except bearings. These features cause a gas turbine to be often used as an exhaust gas turbine that converts pressure energy remaining in exhaust gas emitted from a displacement engine into motive power.
However, rotational speed and load of an engine, when it is used for vehicles such as automobiles, greatly vary depending on operating conditions such as acceleration of a vehicle and slope of roads. This causes large fluctuations in amount of gas emitted from an engine. In particular, a gas turbine substantially deteriorates its efficiency in the range outside of designed gas pressure and flow rate. This causes a gas turbine and an internal combustion engine with an exhaust gas turbine to deteriorate their efficiency under partial load conditions when they are used for vehicles, thus resulting in low fuel economy.
To relieve deterioration of efficiency described above to some extent, Japanese Unexamined Patent Application Publication No. 2001-12252 (also cited in the next paragraph), for example, disclosed a variable nozzle gas turbine that varies angle of vanes constituting nozzles thereof to change overall area of nozzle openings and was used as an automotive turbocharger.